Hi, I''ve recently deployed a Xen 4.1.3 server based on Debian Wheezy for Dom0. The hardware is a dual E5-2630 Xeon machine. I deployed a PVHVM webserver there and I am quite satisfied with it''s performance. I have two SSD drives there and powerful Adaptec controller there and the plan was to place a DB server on another VM and use these SSD drives for that. I wanted to do some baseline benchmarking before the dbserver deployment and then some strange pgbench results came out of that. To cut a long story short, select-only benchmarks on ~300 MB databases (fully fitting in RAM) give results even 10 times worse than expected (!?). I tested PVHVM domU with various 3.2 and 2.6.32 kernels, various core counts and RAM sizes. What''s wierd, I got the same poor results when I run the benchmark on dom0 (in desperation I installed PostgreSQL there), again with various RAM and core count settings. At most I got up to 10k select transactions per second, while on the same hardware using the same dom0 kernel booted up without Xen hypervisor the results were around 100k tps (!?!). Please note that the database fits compeletely in RAM even on a 512 MB RAM dom0/domU (that is one of the variants I tested). There is obviously some bottleneck with cached I/O or maybe more generic problem with RAM access. Hard drive access is completely irrelevant here as the database gets cached in kernel buffers right at the start of the benchmark (which runs for 5 minutes to get more accurate results). There was no point for me in testing the SSD drives in action having observed this strange behaviour. Has anyone observed something like that? Any idea what may be wrong? -- Best regards, Szymon Juraszczyk